The present invention relates to a chip-in-glass fluorescent display device having a semiconductor device disposed inside an envelope thereof; and, more particularly, to a semiconductor device built-in fluorescent display device having a semiconductor device arranged in a space under a supporting member of filament-shaped cathodes.
Generally, a chip-in-glass fluorescent display device includes a semiconductor device such as an integrated circuit (IC) usually incorporating therein a drive circuit and a control circuit, wherein the semiconductor device is installed inside a highly vacuumed envelope of the display device. Such a chip-in-glass fluorescent display device is advantageous in that a module employing the display device can be small-sized and the circuit thereof rarely needs wirings for an external connection.
However, the semiconductor device installed inside the envelope of the above-mentioned fluorescent display device forms a dead space on a display area (i.e., an area for anodes), thereby reducing the display area. In addition, ultraviolet and visible rays incident from an exterior may cause an erroneous operation of the semiconductor device.
To prevent such problems, a prior art provides a chip-in-glass fluorescent display device shown in FIGS. 1A and 1B. To install a plurality of filament-shaped cathodes 50 (simply referred to as filaments hereinafter) at a certain pitch, an anchor 51 for supporting filaments 50 is fixedly provided on a supporting structure 52. Since a semiconductor device 53 is disposed in a space under the supporting structure 52, the loss of display area due to the installation of the semiconductor device 53 can be avoided and the semiconductor device 53 can be protected from the influence of an external light.
The configuration of the above-explained fluorescent display device is described in more detail. The supporting structure 52 of a metal plate has a top plate portion 52a, side plate portions 52b, and base plate portions 52c. The top plate portion 52a is disposed over the semiconductor device 53. Each of the side plate portions 52b is bent down from a side edge of the top plate portion 52a (in a pitch direction of the filaments 50) and serves to produce an installation space of the semiconductor device 53 under the top plate portion 52a. Each of the base plate portions 52c is bent from a lower portion of a corresponding side plate portion 52b and fixed to an anode plate 54.
The anchor 51 has an anchor base portion 51a and a plurality of arms 51b extended therefrom. The anchor base portion 51a is fixed to an upper surface of the top plate portion 52a of the supporting structure 52, wherein each of the arms 51b has a free end portion for fixing an end portion of a filament 50. The free end portion of each arm 51b is upwardly extended with respect to the anchor base portion 51. The filaments 50 with tension therein are stretched above the supporting structure 52 and the anchor base portion 51a with tension applied to each.
However, the prior art fluorescent display device described above suffers from certain drawbacks. That is, since the filaments 50 are disposed above the supporting structure 52 (and the anchor base portion 51a) covering the semiconductor device 53, a gap is present at a relatively great height xe2x80x9cFHxe2x80x9d between the filament 50 and the anode plate 54, thereby deteriorating the brightness of the fluorescent display device.
More specifically, in addition to the thickness of the semiconductor device 53 disposed on the anode plate 54, a space is required between the semiconductor device 53 and the supporting structure 52 and, further, the filaments 50 are also vertically spaced apart from the anchor base portion 51a disposed on the supporting structure 52. Therefore, the height xe2x80x9cFHxe2x80x9d measured from the anode plate 54 to the filament 50 is determined by the above-mentioned thickness and interposed space, wherein a minimum value thereof is usually about 1.3 mm. The relatively great height xe2x80x9cFHxe2x80x9d of the filaments 50 causes insufficient brightness when the fluorescent display device is used in a car in which a low voltage level, e.g., about 12 V, is applied thereto.
Actually, the height xe2x80x9cFHxe2x80x9d of the filament 50 needs to be about 0.9 to about 1.10 mm in case such a chip-in-glass fluorescent display device is employed in a car to be operated at a low voltage level. Moreover, some cases may need the height xe2x80x9cFHxe2x80x9d to be about 1.2 mm even under high voltage driving conditions and, for certain cases, such a conventional fluorescent display device cannot be used at all.
In view of fabricating the supporting structure 52 of the fluorescent display device shown in FIGS. 1A and 1B, it is difficult to bend the side plate portions 52b at a perpendicular angle of 90 degrees with respect to the top plate portion 52a or the base plate portions 52c. Consequently, after the supporting structure 52 is fixed on the anode plate 54, each of the side plate portions 52b is slanted as shown in FIG. 1B, thereby shortening the length of the top plate portion 52a along the pitch direction of the filaments 50. This results in reducing an effective area in the top plate portion 52a for mounting the anchor base portion 51a. As a result, the number of the filaments 50, i.e., a width xe2x80x9cFWxe2x80x9d of the arranged filaments 50, is limited and, therefore, a display area cannot be enlarged in the pitch direction of the filaments 50.
On the other hand, the anchor 51 serves to apply a tension to the free end portion of each arm 51b in the pitch direction of the filaments 50. Since, however, the area of the top plate portion 52a is small and the number of the arranged filaments 50 is limited, a dead space is formed at an end side along the pitch direction of the filaments 50 (at a right region in FIG. 1B). Therefore, the display area of the conventional fluorescent display device is also decreased in the pitch direction of the filaments 50.
It is, therefore, an object of the present invention to provide a chip-in-glass fluorescent display device implementing a high brightness and a wide display area in spite of a low voltage driving condition.
In accordance with a preferred embodiment of the present invention, there is provided a fluorescent display device including an anode plate and a semiconductor device arranged thereon, wherein the anode plate forms a portion of an envelope of the display device and has an anode on an inner surface thereof, the display device further including: a supporting structure disposed on the anode plate, the supporting structure having a top plate portion overlapping the semiconductor device; and a tensioning member, disposed on the top plate portion of the supporting structure, for arranging a plurality of filament-shaped cathodes at a pitch between the semiconductor device and the top plate portion.